1. Field of the Invention
This invention relates generally to the construction of concrete slabs. More particularly, the invention relates to an improved joint edge assembly that protects the joint edges, permits more accurate alignment of the joint edge assembly members, and allows the joint edges to both self-open and move laterally with respect to the opposite joint edge as the concrete shrinks during hardening.
2. Related Art
For logistical and technical reasons, concrete floor slabs are made up of a series of individual blocks. The interface where one block meets another is termed a joint. Freshly placed concrete shrinks considerably as it hardens as the chemical reaction between the cement and the water occurs, i.e., hydration. As the concrete shrinks, tensile stress accumulates in the concrete. Therefore, the joints should be free to open and thus allow shrinkage to occur without damaging the slab.
The joint openings, however, create discontinuities in the slab surface, which can cause the wheels of forklift trucks and other vehicles to impact the joint edges and chip small pieces of concrete from the edge of each slab, particularly if the joint edges are not aligned. This damage to the edges of slabs is commonly referred to as “joint spalling.” Joint spalling often interrupts the normal working operations of many facilities by slowing down forklift and other truck traffic, and/or causing damage to trucks and the carried products. Severe joint spalling and uneven joints can even cause loaded forklift trucks to be overturned and can be dangerous to employees. Moreover, joint spalling can be very expensive to repair.
For these reasons, it is advantageous to protect the joint edges against spalling with steel bars or angles. Commonly used details illustrating the use of hot rolled steel bars (or angles) are shown in the American Concrete Industry (ACI) technical manuals 302 and 360. However, the standard installation procedure for these steel bars or angles is both time-consuming and expensive. The conventional procedures typically includes the following steps: (1) a temporary edge form is erected; (2) the first bar (or angle) is attached to the edge form; (3) the first concrete slab is cast; (4) the form is removed; (5) the second bar (or angle) is tack welded to the first; (6) the second concrete slab is cast; and (7) the tack welds are removed by grinding. Importantly, the quality control of the tack welding and the timing of the tack weld grinding are critical to the joint performance. If a weld is not completely removed by grinding, or if grinding is not completed shortly after the second slab is cast, then the joint remains locked together and tensile stress accumulates in the slabs, which often leads to unacceptable slab cracking. Furthermore, if the joint edge members are not evenly aligned during the tack welding, a permanent slab discontinuity may result in the finished product, which may also lead to increased impact with the joint edges.
For at least the foregoing reasons, an improved joint edge assembly that protects the joint edges of the concrete slab, permits more accurate alignment of the joint edge assembly members, and allows the joint edges to both self-open and move laterally with respect to the opposite joint edge as the concrete shrinks during hardening would be desirable.